Oil cooling a motor with transformer oil/dielectric fluid - the next frontier?

[neptronix]

Mineral oil sounds good except...

- low materials compatibility, known to eat plastic and eventually delaminate circuit boards over a long period of time
- breaks down / oxidizes faster than most cooling oils
- smoke point at 135C, kind of low for a hub motor
- more toxic
- carcinogenic if not extremely pure

A lot of people building high performance computers who have used mineral oil had components destroyed after a number of years and concluded is it not worth it.

I say that since we have close to the same variety of materials as a PC, mineral oil is not suitable long term for a hub motor.

Looking for something like opticool or even better.

 

[scianiac]

I think it's been suggested before but assuming you check for any use of silicones inside the motor DOT5 brake fluid seems like a pretty good option all things considered. Very low viscosity even at low temperatures (lower than ATF but a decent bit, slightly lower than opticool at 50C), very good compatibility, maybe compatible with everything except silicones, relatively safe. Only downside I see is the same with other oils which is brake rotor contamination.

Now if the compatibility of silicone oil works it may be easy enough to find something more pure than DOT5 (I don't know if there are really many additives normally used in it) with the same or lower viscosity, silicone shock oils perhaps.

 

[neptronix]

According to EEVblog, silicone oil will screw up rubber and plastic ( per some manufacturers of the stuff ):
Submerged mineral oil PC - but EE what would say on it? Finally... - Page 1

Silicone oil also has pretty low heat transfer properties.
I can only find one report of using silicone oil in computer cooling and it's in the above thread.

Brake fluid, unknown. I read that it has a high propensity to absorb water from air, which could make it conductive. It comes in differing formulations which have varying materials compatibility. I dunno if this would be suitable.

Opticool for comparison:

 

[Dui ni shuo de dui]

Brake fluid, unknown. I read that it has a high propensity to absorb water from air, which could make it conductive. It comes in differing formulations which have varying materials compatibility. I dunno if this would be suitable.

Brake fluid is extremely corrosive. I wouldn't put it anywhere near the motor.

Maybe I missed it but I haven't seen the most obvious option : regular engine oil.
It shouldn't harm other materials very much, it's widely available for cheap, it doesn't degrade, it prevents rust of the core (I've red some people talking about distilled water earlier... well the iron core would rust even faster in distilled water than regular water, it would completely destroy the motor in a matter of days/weeks!), it's a very poor electric conductor, and last but not least, some relatively thin motor oils are available, such as 0W20.

Sounds like something very easy to try for anyone who'd like to experiment.

 

[scianiac]

DOT5 brake fluid is silicone oil, it is quite different than all the other flavors. Also as far as I can tell from research silicone oil is very compatible with all rubbers except silicone and Fluorosilicone. So as long as we check for and replace any silicones used in the motor, which doesn't sound that hard, it should be good. Also it seems like the thermal conductivity of silicone oil slightly better than opticool at 40C and slightly worse at 100C but pretty close either way.

All that being said if opticool is so great why don't we just use a similar product, been awhile since I skimmed through the thread but if I recall it was that it was too hard to get but a quick search for "Dielectric Coolant Fluid" comes up with some options at reasonable prices and while they are all different and some research would be needed they seem to be for the same application.

 

[nicobie]

things that can go boom, and there ya have it, the transformation of money into noise and smoke

I must say, that sounds like fun!

 

[DaLanMan]

I was literally a professional operator at one point. it was a tonne of fun, still keep in touch with most the guys (well, ones that are still with us, not a lot of old guys left it seem).

 

[Bullfrog]

Justin (Grin Tech owner/operator) suggested an alcohol might be a good cooling fluid. After his suggestion, I tried distilled water with Motul MoCool as a corrosion inhibitor in my MAC and it worked quite well. Nice thing about using my mixture was if it leaked on my brake disc, it didn't appreciably affect the braking performance like ATF did.

Geared hub motors like a MAC have a different requirement than Direct Drive hub motors like the Leaf because you need about five times as much cooling liquid to thermally connect the windings to the shell for the Geared motors so viscosity can be a bigger problem for the Geared motor.

 

[scianiac]

Justin (Grin Tech owner/operator) suggested an alcohol might be a good cooling fluid. After his suggestion, I tried distilled water with Motul MoCool as a corrosion inhibitor in my MAC and it worked quite well. Nice thing about using my mixture was if it leaked on my brake disc, it didn't appreciably affect the braking performance like ATF did.

I was thinking about both of those the other day but was worried that the water/coolant may cause electrical conductivity problems, although I suppose that depends how well things are sealed which wouldn't be that hard and how much is in there. The alcohol I think would work quite well if you had a way to cool it well enough, without enough cooling like a vent to a radiator the alcohol would evaporate too fast. But if you could recondense the vapor the whole system could be a phase change cooling system, although even that may have to operate at some amount of pressure now that I think about it.

 

[Cowardlyduck]

Many years ago I did an experiment with what I had on hand at the time which was chainsaw oil. Ran a '200W' hub at over 800W for many kms without issue. It did leak a bit, but not enough to cause problems.
In the end that motor overheated from a badly rubbing hub brake shoe transferring heat into the motor....ironically I hadn't noticed it was rubbing due to the increased power available.

Cheers

 

[A-DamW]

Many years ago I did an experiment with what I had on hand at the time which was chainsaw oil. Ran a '200W' hub at over 800W for many kms without issue. It did leak a bit, but not enough to cause problems.
In the end that motor overheated from a badly rubbing hub brake shoe transferring heat into the motor....ironically I hadn't noticed it was rubbing due to the increased power available.

Cheers

Was that 2-stroke oil or bar and chain oil?

 

[Cowardlyduck]

Was that 2-stroke oil or bar and chain oil?

Bar/chain oil. Super thick, super sticky, but it did work surprisingly well. I guess that makes some sense given it's partially designed to keep the chain cool.

Cheers

 

[Marc S.]

Really? You guys still discussing alternative oil for geared hub motors in 2024?

Whats wrong with ATF? I hate the smell of ATF like the next guy (only jet fuel smells worst) but ATF has the right viscosity and got all the necessary additives (foam inhibitors, friction inhibitors, etc, etc) to make it the best oil for the job.

 

[Cowardlyduck]

Really? You guys still discussing alternative oil for geared hub motors in 2024?

Whats wrong with ATF? I hate the smell of ATF like the next guy (only jet fuel smells worst) but ATF has the right viscosity and got all the necessary additives (foam inhibitors, friction inhibitors, etc, etc) to make it the best oil for the job.

Reminiscing would be more accurate...what I mentioned above was done in 2014 or 2015. Point was that it worked and worked well...I would do it again if I didn't want to bother getting ATF just like last time.

Cheers

 

[neptronix]

Really? You guys still discussing alternative oil for geared hub motors in 2024?

Whats wrong with ATF? I hate the smell of ATF like the next guy (only jet fuel smells worst) but ATF has the right viscosity and got all the necessary additives (foam inhibitors, friction inhibitors, etc, etc) to make it the best oil for the job.

Personally,
- If i'm going to add something is going to drip everywhere, i want it to have low toxicity. A few laps of ATF can kill a dog.. i have two cats in my home.
- I want to be sure the fluid won't destroy parts of the motor over a period of 5 years. I want the highest materials compatibility i can get.

 

[Dui ni shuo de dui]

Personally,
- If i'm going to add something is going to drip everywhere, i want it to have low toxicity. A few laps of ATF can kill a dog.. i have two cats in my home.

There are automatic transmissions everywhere, many of then leaking, but cats and dogs are mostly fine.
I think you're overthinking it a little too much, the real risk is getting oil on the tire, bu if it's sealed properly this is unlikely to happen.

- I want to be sure the fluid won't destroy parts of the motor over a period of 5 years. I want the highest materials compatibility i can get.

There is only one sure way to know the reliability: to try and see how it goes.

I don't think there will be any problem with it, we're all fine with the idea of leaving the motor filled with air and moisture which corrodes the magnets and more importantly the laminated cores, we don't even think of it being wrong when it's one of the main motor death causes. At least adding oil will solve this issue for sure, all the rest is hypothetical.

 

[DaLanMan]

Never seen much on animals and transmission fluid, i have however heard inumerous times that leaving anitfreeze out is dangerous to animals, and from having to chase my dogs off the gravel where I rinse out things when I am done with them (it is a ghetto settling tank. 22x30x8 pan sunk in the ground and filled with gravel. I clean it out properly once a year and so far not even discoloured gravel, I am just paranoid about pollution)

Also.. I have rat issues due to living next to farmland. They are currently self regulating because one chewed into an anti-freeze container and died... so now that container is on it's side, on the top shelf with a little rat be gone in it. Hey, I don't like killing animals but if they are gonna move in, they gotta pay rent.

 

[neptronix]

OK, i looked into Bullfrog's suggestion on motul mocool.
Link to MSDS

MSDS states there are 3 ingredients, one which makes up ~1% of the mocool mixure is significantly toxic. The others are not so bad and close to opticool.

I found some research about a lubricant that was 90% water. It states that the coefficient of friction is lower. The stuff looks impressive.



I'm surprised that bullfrog hasn't encountered any issues with gears using mostly water and mocool, neither which i think have lubricating properties. Add a small amount of lubricant and apparently you're outperforming synthetic oil..?


There appear to be a number of companies making water based lubricants/coolants with high materials compatibility and safety. Here is one i could find with the most detail.

Water-based lubricant provides new pathway for electric vehicle lubrication

Supposedly they have tested and vetted for materials compatibility in the applications. More info in their giant brochure

This stuff is also very new, about a year old.





Any thoughts?

 

[neptronix]

Long term tests published by Total energies

 

[neptronix]

Is your lubricant running low? Just add water - Drives and Controls Magazine



"However, until now, he adds, water has been of limited use as a lubricant because it is “subject to certain physical and biological limitations – like evaporation and freezing points, oxidation or microbiological growth”. But “by means of additives in the lubricant or technical solutions at the component concerned, these limits can be shifted, and the water-specific effects rendered beneficially usable. With a water-based product concept, we’ve even been able to reduce the friction involved far enough to bring the range of ‘super-lubricity’ within reach.”

 

[marka-ee]

Interesting thread. My little 250 watt planetary reduction hub motor recently threw one of its four magnets when it got too hot so I actually used red high temperature RTV silicone to glue it back in place. The epoxy that I can easily get are only rated to 100C, while this red silicone sealer is rated at 300C .Now that I'm thinking of using DOT 5 silicone-based brake fluid as a heat conduction mechanism, I'm worried because some articles say that silicone brake fluid actually does attack the RTV silicone sealer, but I get different opinions depending on what article I see. So far the silicone fluid seems more compatible with motor winding enamel and other possible plastics that might be inside the motor, although mine really doesn't have any plastic at all because it's all metal. No HAL sensors either. What do you guys think about DOT 5? It should be fairly easy to get and hopefully fairly compatible.

 

[Dui ni shuo de dui]

Interesting thread. My little 250 watt planetary reduction hub motor recently threw one of its four magnets when it got too hot so I actually used red high temperature RTV silicone to glue it back in place. The epoxy that I can easily get are only rated to 100C, while this red silicone sealer is rated at 300C .Now that I'm thinking of using DOT 5 silicone-based brake fluid as a heat conduction mechanism, I'm worried because some articles say that silicone brake fluid actually does attack the RTV silicone sealer, but I get different opinions depending on what article I see. So far the silicone fluid seems more compatible with motor winding enamel and other possible plastics that might be inside the motor, although mine really doesn't have any plastic at all because it's all metal. No HAL sensors either. What do you guys think about DOT 5? It should be fairly easy to get and hopefully fairly compatible.

Honestly, no one here knows for sure because most people talk about trying but very few actually try it.
The only way for you to know for sure is to try and see.

Personnally if I were to try I'd just use regular engine oil or transmission fluid. At the speeds we are running our motors I don't think there should be any significant issue with viscosity, and the oils used in engines are developped to be non corrosive to pretty much any materials. For me the only real challenge is to make sure there won't be any leak ever.

Anyway, I think there is way too much overthinking in this thread, what we need now is some actual experiences, it's been 4 years since the thread has been created and so far not much to show !
I think I'm gonna try and experiment this with my old 2000W QS205 motor before the end of the year, only issue being its a lot of work since I'd have to install a temp sensor, then run the motor for a few days to get data, then add the oil, seal the motor and test again to see the difference. I just need to find some time and motivation to do that.

I did try ferrofluid on my QS273 and it was working well. Temperatures were rising normally during acceleration, but they were coming down a lot faster afterwards. The casing was much hotter than before, indicating that the heat transmission from the stator was significantly better. In my opinion it might work even better with oil, because it will cover everything instead of just the magnetic parts. It's probably good to have oil all over the motor side plates, it should increase heat conductivity on a much bigger surface. Ferrofluid is nice, but it directs all the heat through the magnets, which are the most heat sensitive components of the motor.

 

[marka-ee]

I think viscosity could be a factor in geared hub motors like the one I'm using in this small folding bike. The ratio that it's achieving is about 12 to 1. That runs at about 5000 rpm for the motor's rotor with the bicycle going 35 kilometers per hour.. At that RPM, the viscosity could be a significant drag. The direct drive is a different matter entirely. I'm gonna try to get silicon oil but if I can't get that I'll try paraffin oil.

 

[Ianhill]

I get he is using dc brushed motors and its not the same but the overall conclusion remains the same, any moving part submerged in coolant will encounter drag and the increased effort needed to overcome said drag with power that in turn creates more heat and comes from a battery thats limited by range. already theres no room to throw away power even on a slower rotating larger massed hub motor the same applys.

Riddle me this why have all motors that use coolants have passages not full submerging the rotor its simply because its either better to not cool at all and oversize the motor or use a more advanded design that has cooling passages.


Is it possible to run a motor with oil in it yes definitely, can a working production example be mentioned ? I dont know of one and would love to see a detailed experiment on before and after and see if they keep it that way.

 

[marka-ee]

Interesting video. I kind of felt sorry for the motor. Anyhow, at 5000 RPM, which is my approximate RPM that the rotor would be spinning, the drag wasn't really so bad. Plus, the rotor has a lot more streamlined cross-section compared to the typical small brushed DC motor, which has almost impellers. So I think it's still worth a try with some kind of cooling fluid. I'm not in a position to replace the whole hub motor for the 16-inch rim. Plus, they're very hard to find, and you never know what speed you're going to get out of it because the Chinese always exaggerate their specs. I may just use some synthetic ATF since it's easy to get and cheap. I wonder if I should add some powdered moly to it? This would give it enhanced lubricanticity properties, I think, which might be good for this little mini hub.